Method for controlling plasma processing apparatus

ABSTRACT

There is provided a method for controlling a plasma processing apparatus that eliminates a preliminary study on a resonance point while maintaining a low contamination and a high uniformity even in multi-step etching. In a method for controlling a plasma processing apparatus including the step of adjusting a radio frequency bias current carried to a counter antenna electrode, the method includes the steps of: setting a reactance of a variable element to an initial value; detecting a bias current carried to the counter antenna electrode; searching for a maximum value of the detected electric current; and adjusting a value of the reactance of the variable element from the maximum value to the set value and then fixing the value.

CLAIM OF PRIORITY

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2013-024207, filed Feb. 12,2013, and Application No. 2013-112562, filed May 29, 2013, the entirecontents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling a parallelplate plasma processing apparatus that manufactures semiconductordevices and Micro Electro Mechanical System (MEMS) devices.

2. Description of the Related Art

For micro-fabrication of grooves in a space width of 10 nm and aspect of15 or more on stacked films such as silicon, silicon oxidize, andsilicon nitride, micro-fabrication is performed mainly using a parallelplate plasma processing apparatus that generates plasma in a regionsandwiched between an upper electrode and a lower electrode. For theparallel plate plasma source, a capacitive coupling plasma (CCP)apparatus is used as well as a magnetic field VHF plasma apparatus isused including a supply for a VHF wave of 200 MHz and a magnetic fieldgenerating coil.

This magnetic field VHF plasma apparatus has a structure below. Theupper electrode of the magnetic field VHF plasma apparatus includes afunction of emitting VHF waves for plasma generation. For an upperelectrode member, a dielectric ceramic material such as silica, yttria,and sapphire glass or a material that an aluminum material or stainlesssteel material is coated with a dielectric ceramic material is used fora surface contacting plasma, from viewpoints of contamination andforeign substances. Moreover, the plasma generation distribution and thein-plane distribution of the etching rate can be controlled using amagnetic field from a magnetic field generating coil. A radio frequencybias can be applied to the lower electrode on which a wafer is placedfor anisotropy etching. See Japanese Patent Application Laid-OpenPublication No. 2007-59567.

On the other hand, in the CCP etching apparatus, a plasma processingapparatus is disclosed for improving uniformity, which includes acircuit that adjusts electrical characteristics (impedance) on thecounter electrode side on which a bias frequency is applied so as toprevent an electric current flowing into the counter electrode side frombecoming the maximum. See Japanese Patent Application Laid-OpenPublication No. 2011-82180, which discloses a control method in which abias current is adjusted to a half of the maximum electric current ormore.

SUMMARY OF THE INVENTION

In order to perform highly uniform etching with much less contaminationusing a magnetic field VHF plasma etching apparatus including adielectric ceramic on the upper electrode, the inventors conductedcontrol described in Japanese Patent Application Laid-Open PublicationNo. 2011-82180 in which a counter bias control mechanism is mounted onthe upper electrode side, including a resonance coil that cancelsreactance caused by the electrostatic capacitance of the dielectricceramic and a variable capacitance. As a result, it was revealed thatthe following problems arise in that in the case where a multi-layerfilm is etched in multiple steps, the etching conditions are varied inthe individual steps, and thus the magnitude of the variable capacitanceto resonate and the absolute value of a counter bias current arechanged, and in that when a preliminary study is conducted beforeprocessing as the measures for these changes, CoO is increased due tothe use of a dummy wafer and a preparation is prolonged until processingtime, for example.

Moreover, it was revealed that in the case of using control described inJapanese Patent Application Laid-Open Publication No. 2011-82180 in anend point determination step, since the counter bias current and theresonating reactance themselves are changed in the step, the biascurrent value goes out of the resonance point in the midway point of thechange, the plasma distribution is changed, and the in-planedistribution of the substrate error selection ratio is degraded.

A first object of the present invention is to provide a method forcontrolling a plasma processing apparatus that eliminates a preliminarystudy on a resonance point while maintaining a low contamination and ahigh uniformity even in multi-step etching. Moreover, a second object ofthe present invention is to provide a method for controlling a plasmaprocessing apparatus that follows changes in the resonance point orchanges near the set resonance point and enables highly uniform etchingof a multi-layer film even in a so-called transient state in which acounter bias current or plasma impedance is changed in an ignition step,an end point determination step, and other steps.

In order to solve the problems, configurations and process proceduresdescribed in the appended claims, for example, are adopted.

The present specification includes a plurality of means for solving theproblems. One example is a method for controlling a plasma processingapparatus including a plasma processing chamber configured toplasma-process an object to be processed, a first flat electrodeconfigured to emit a radio frequency into the plasma processing chamber,a first radio frequency power supply configured to supply radiofrequency power to the first electrode, a second electrode opposite tothe first electrode and on which the object to be processed is placed, asecond radio frequency power supply configured to supply radio frequencypower to the second electrode, and a control mechanism configured tocontrol a radio frequency current carried through the first electrode ora radio frequency voltage applied to the first electrode, the methodincluding: a first step of setting a reactance of a variable elementincluded in the control mechanism to an initial value; a second step ofdetecting the radio frequency current or the radio frequency voltage;and a third step of setting the reactance of the variable element to areactance value so that the radio frequency current takes a maximumvalue or the radio frequency voltage takes a maximum value and fixingthe reactance of the variable element to the set reactance value.

Moreover, another example is a method for controlling a plasmaprocessing apparatus including a plasma processing chamber configured toplasma-process an object to be processed, a first flat electrodeconfigured to emit a radio frequency into the plasma processing chamber,a first radio frequency power supply configured to supply radiofrequency power to the first electrode, a second electrode opposite tothe first electrode and on which the object to be processed is placed, asecond radio frequency power supply configured to supply radio frequencypower to the second electrode, and a control mechanism configured tocontrol a radio frequency current carried through the first electrode ora radio frequency voltage applied to the first electrode, the methodincluding: a first step of detecting a phase difference between a radiofrequency current carried through the second electrode and a radiofrequency current carried through the first electrode or a phasedifference between a radio frequency voltage applied to the secondelectrode and a radio frequency voltage applied to the first electrode;and a second step of controlling a reactance of a variable elementincluded in the control mechanism so that the detected phase differencetakes a phase difference value matched with a maximum value of the radiofrequency current carried through the first electrode or a maximum valueof the radio frequency voltage applied to the first electrode.

According to the present invention, it is possible to provide a methodfor controlling a plasma processing apparatus that eliminates apreliminary study on a resonance point while maintaining a lowcontamination and a high uniformity even in multi-step etching.

Moreover, it is possible to provide a method for controlling a plasmaprocessing apparatus that follows changes in the resonance point orchanges near the set resonance point and enables highly uniform etchingof a multi-layer film even in a so-called transient state in which acounter bias current or plasma impedance is changed in an ignition step,an end point determination step, and other steps.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become fully understood from the detaileddescription given hereinafter and the accompanying drawings, wherein:

FIG. 1 is a schematic cross sectional view of the overall structure of adry etching apparatus (a magnetic field VHF dry etching apparatus) foruse in performing a method for controlling a plasma processing apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a circuit block diagram of a counter bias control mechanism ofthe dry etching apparatus illustrated in FIG. 1;

FIG. 3 is a flowchart for explaining control of the method forcontrolling a plasma processing apparatus according to the firstembodiment of the present invention;

FIG. 4 is a graph of the dependence of a counter bias current on avariable capacitance in the dry etching apparatus illustrated in FIG. 1;

FIG. 5 is a graph of the dependence of the phase difference between acounter bias current and a radio frequency bias current on a variablecapacitance in the dry etching apparatus illustrated in FIG. 1;

FIG. 6 is a flowchart for explaining control of a method for controllinga plasma processing apparatus according to a second embodiment of thepresent invention;

FIG. 7 is a schematic cross sectional view of the overall structure ofanother dry etching apparatus (a CCP etching apparatus) for performingthe method for controlling a plasma processing apparatus according tothe first and second embodiments of the present invention;

FIG. 8 is a schematic cross sectional view of the overall structure of adry etching apparatus (a magnetic field VHF dry etching apparatus) foruse in performing a plasma processing method according to a thirdembodiment of the present invention;

FIG. 9 is a circuit block diagram of a counter bias control mechanism ofthe dry etching apparatus illustrated in FIG. 8;

FIG. 10 is a graph of the dependence of a counter bias current on avariable capacitance in the dry etching apparatus illustrated in FIG. 8;

FIG. 11 is a graph of the in-plane distribution of the oxidization filmetching rate on a shower plate when a counter bias control mechanism isresonating and not resonating in the dry etching apparatus illustratedin FIG. 8;

FIG. 12 is a time sequence of changes in monitor values in cleaning andthe control of a variable capacitor in the dry etching apparatusillustrated in FIG. 8;

FIG. 13 is a block diagram of an end point determination circuit forplasma processing according to the third embodiment of the presentinvention;

FIG. 14 is a graph of the dependence of the oxidization film etchingrate on the RF bias power at the center point of the shower plate whenthe counter bias control mechanism is resonating and not resonating inthe dry etching apparatus illustrated in FIG. 8; and

FIG. 15 is a cross sectional view of a dry etching apparatus with noelectromagnet for performing another plasma processing method accordingto the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described withreference to FIGS. 1 to 4. First, a plasma processing apparatus mountedwith a counter bias control mechanism that embodies a bias currentcontrol method in a method for controlling a plasma processing apparatusaccording to the embodiment will be described. FIG. 1 is a verticalcross sectional view of a parallel plate magnetic field VHF dry etchingapparatus.

A vacuum container of the dry etching apparatus includes an etchingchamber 108 for a plasma processing chamber, an earth internal cylinder107, a silica top plate 111, a VHF radiation antenna 115, a vacuum pump,and a pressure control valve (both of them are not illustrated in FIG.1).

Etching gases pass through a mass flow controller and a stop valve (bothof them are not illustrated in FIG. 1), and pass through a gas inletport A 109 and a gas inlet port B 112. The gases are distributed whilepreventing the gases from being mixed with each other using a gasdistribution plate 114, and introduced from regions of a shower plate116 concentrically divided into two parts into the etching chamber. Thegases thus introduced are dissociated from each other by energy ofelectromagnetic waves applied from a plasma generating unit, and plasmais generated and maintained.

This plasma generating unit includes a source power supply 101 of a VHFwave of 200 MHz, a source electromagnetic wave matching unit 102, and amagnetic field generating unit formed of an electromagnet A 105 and anelectromagnet B 106. These two electromagnets are used to uniformize theplasma generation distribution. The generated magnetic field is at 10 mTor less near the shower plate 116. VHF waves oscillated from the sourcepower supply 101 pass through the source electromagnetic wave matchingunit 102, and are introduced into the VHF radiation antenna 115 at aposition opposite to a wafer stage 120. The VHF radiation antenna 115 iselectrically isolated from the etching chamber 108 using the silica topplate 111.

An Si wafer (an object to be processed) 117 is placed on the wafer stage120, including a stack of etched materials and mask materials such as asilicon oxide film, silicon nitride film, Poly-Si (polysilicon) film,resist film, anti-reflective film, TiN film, tungsten film, Ta compoundfilm, and Hf oxide film. The wafer stage 120 includes a focus ring 118and a susceptor 119 in a ring shape disposed as covering the outercircumferential side and the side wall of the surface on which the Siwafer 117 is placed. The wafer stage 120 can control a plurality ofportions on the wafer stage 120 at different predetermined temperaturesusing a plurality of temperature control units, for example, (notillustrated in FIG. 1). The wafer stage 120 applies a direct currentvoltage ranging from −2,000 to +2,000 V generated using an electrostaticchuck (ESC) direct current power supply 122 to electrostatically chuckthe Si wafer 117 in etching processing, fills He of an excellent heattransfer efficiency in a gap between the Si wafer 117 and the waferstage 120, and controls the back surface pressure of the Si wafer 117.For the shower plate 116, silica or yttria was used, which havecorrosion resistance against gasses and do not cause foreign substanceemission. Since the shower plate 116 is in intimate contact with the gasdistribution plate 114 and the VHF radiation antenna 115 using screws,for example, an excessive temperature increase can be suppressed byadjusting the temperature of a cooling medium for the VHF radiationantenna 115.

The wafer stage 120 is connected to an RF bias matching unit 121 and toa 4-MHz RF bias power supply 123 that leads ions from plasma to the Siwafer 117 and controls ion energy.

Such an RF bias power supply including a time modulation (sometimesdenoted as TM) function was used for the RF bias power supply 123, inwhich power can be outputted in a range of about one watt at the lowestto about two kilowatts at the maximum equivalent to the emission ofcontinuous sine waves to an object to be processed in a diameter of 12inches and on-off modulation is performed in a range of one hertz to tenkilohertz in order to obtain the effects of a reduction in charge updamage (electron shading) and improved vertical processability.

A radio frequency bias current applied to the wafer stage 120 propagatesthrough the inside of plasma toward the earth internal cylinder 107disposed as an earth on the inner wall of the etching chamber 108through a plasma sheath on the Si wafer 117. For the earth internalcylinder 107, such a conductive material is used as a conductivematerial of a low contamination or as a conductive material including athermal sprayed material of a low reactivity with etching plasma throughwhich a radio frequency passes, in order to reduce contamination in theapparatus and foreign substances.

In the parallel plate magnetic field VHF etching apparatus, in theembodiment, a counter bias control mechanism 104 is mounted through afilter unit 103 in order that a bias is transmitted to the VHF radiationantenna 115 side opposite to the wafer stage 120 to control the degreeof confinement of the bias electric field for improving etchinguniformity. The filter unit 103 includes a highpass filter (HPF) thatprevents an RF bias of 4 MHz and the third-order harmonic of the RF biasfrom passing on the source power supply side and a lowpass filter (LPF)that flows only an RF bias frequency to the earth side. It is noted thata reference numeral 110 denotes a cooling medium inlet, a referencenumeral 113 denotes a cooling medium outlet, a reference numeral 124denotes a radio frequency bias current detecting unit, a referencenumeral 125 denotes a wafer stage elevating mechanism, a referencenumeral 126 denotes a silica ring, a reference numeral 127 denotes aresonance control circuit, a reference numeral 128 denotes a yoke, areference numeral 131 denotes an EPD (End Point Detector) window, and areference numeral 133 denotes a shield plate.

FIG. 2 is a diagram of the configuration of the counter bias controlmechanism 104. The counter bias control mechanism 104 is configured of aserial resonant portion formed of a resonant coil 201 of low resistancethat hardly generates heat even at the maximum electric current at an RFbias of 4 MHz and a variable capacitor 202 having a moderate withstandvoltage, a counter bias current detecting circuit 203, and a resonancecontrol circuit 127. In consideration of the electrostatic capacitance(C_(sp)) of the silica shower plate 116 and the electrostaticcapacitance (C_(sh)) of a sheath formed on the shower plate, theinductance (L) of the resonant coil 201 and the electrostaticcapacitance (C_(v)) of the variable capacitor 202 are selected using therelationship between Equations (1) to (3).

$\begin{matrix}{X_{V} = {{\omega\; L} - {\frac{1}{\omega}\left( {\frac{1}{C_{Sh}} + \frac{1}{C_{sp}}} \right)}}} & (1)\end{matrix}$

Here, ω is the angular velocity of the RF bias frequency. X_(v) is inthe relationship in Equation (2) where the capacitance is C_(v) in thecase where the variable reactance element is a capacitor, whereas X_(v)is in the relationship in Equation (3) where the inductance is L_(v) inthe case where the variable reactance element is a coil.

$\begin{matrix}{X_{V} = {{\omega\; L} - {\frac{1}{\omega}\left( {\frac{1}{C_{Sh}} + \frac{1}{C_{sp}} + \frac{1}{C_{v}}} \right)}}} & (2) \\{X_{V} = {{\omega\left( {L_{V} + L} \right)} - {\frac{1}{\omega}\left( {\frac{1}{C_{Sh}} + \frac{1}{C_{sp}}} \right)}}} & (3)\end{matrix}$

Moreover, a plurality of sets of a harmonic short circuit coil 204 and aharmonic short circuit fine tune capacitor 205 according to the harmonicorder is inserted in parallel with a circuit formed of the resonant coil201 and the variable capacitor 202, and the impedance of a harmoniccomponent generated when passing through the plasma sheath on the VHFradiation antenna 115 can also be reduced, so that etching can beuniformized for wider plasma conditions. Furthermore, the electriccurrent values of a plurality of harmonic components are monitored usinga harmonic current detection circuit 207, so that information about theplasma density and the electron temperature can be obtained as well, anda change in the state of the apparatus can be detected more accurately.It is noted that a reference numeral 206 denotes an automatic matchingunit, and a reference numeral 209 denotes an automatic harmonic matchingunit.

The embodiment relates to a bias current control method using thecounter bias control mechanism 104 disposed on the parallel plate plasmaprocessing apparatus thus configured. FIG. 3 is a control flow forexplaining a bias current control method of a method for controlling aplasma processing apparatus according to the embodiment. Moreover, FIG.4 is the dependence of the counter bias current on the variablecapacitor capacitance. When the etching sequence is started (S1), anapparatus control PC sends signals of a preset position 403 and a targetdelta value 406 for the variable capacitor (the variable element) 202 tothe resonance control circuit 127, and the variable capacitor 202 isadjusted to the preset position (S2). At this time, in the case wherethe apparatus control PC does not instruct the automatic control mode,the variable capacitor 202 is fixed at the preset position 403 inetching. On the other hand, in the case where the apparatus control PCinstructs the automatic control mode, the RF bias power supply 123outputs power (S3). Automatic control is then started from a point atwhich the antenna bias current exceeds a threshold at the counter biascurrent detecting circuit 203 (S4), and the variable element 202 startsthe operation toward a resonance point 405 (S5).

FIG. 4 is measured data of a typical tendency of the counter biascurrent showing manners of the counter bias current and the variablecapacitance. It is shown that since the point at which the bias currentbecomes the maximum is the resonance point, the counter bias currentvalue takes the maximum value with respect to the capacitance of thevariable capacitor 202. Moreover, the capacitance of the variablecapacitor at the maximum value and the maximum value of the counter biascurrent are changed in the range of about 50 pF when the electricalcapacitance (C_(sh)) of the sheath formed on the shower plate ischanged, that is, when the plasma conditions (the output power of thesource power supply 101, the processing pressure, and the power of theRF bias power supply 123, for example) are changed. Furthermore, whenthe electrostatic capacitance becomes greater than that at the resonancepoint, the bias current is suddenly reduced, and the etching ratedistribution is similarly suddenly degraded as well. Thus, preferably,automatic control is started as the electrostatic capacitance at thepreset position 403 is set lower than that at the resonance point 405.It is noted that a reference numeral 401 denotes the peak-to-peakcurrent of the counter bias, and a reference numeral 404 denotes acounter bias current value when automatic control is finished.

Therefore, in the embodiment, the preset position 403 is selected atwhich the electrostatic capacitance is smaller than the electrostaticcapacitance at the resonance point 405 (greater as reactance) and thebias current is a threshold current or more in starting. When the biascurrent exceeds the set threshold (S4), the resonance control circuit127 changes the capacitance of the variable capacitor in the directionin which the bias current is increased. The electrostatic capacitanceposition at which the bias current is turned into a reduction is storedas the resonance capacitance (S6), the capacitance is moved from theposition to the capacitance by the set target delta value 406 (S7), andthe capacitance is fixed at the position in etching processing (S8).After that, the radio frequency bias is turned off, the capacitance ofthe variable capacitor 202 is reset when the counter bias current islower than the set threshold (S10), and a series of the operations isfinished (S11).

The description above is the operation in the first step in which plasmadischarge is intermitted in every step. In the case where the etchingconditions are changed as plasma discharge is continued, the variablecapacitor 202 is fixed, and automatic matching is finished (S8), and atrigger signal outputted at the timing at which the process goes to thesubsequent step is then received from the apparatus control PC (S9). Inthe case where discharge is continued, the variable element is adjustedto the preset value in the in the subsequent step (S2), and theautomatic control flow is again started in the midway point. In therestarting, the preset value in the step in which discharge is continuedis set to a value smaller than the capacitance of the variable capacitorat the resonance point, so that it is possible to improve thedegradation of uniformity and stability after discharge is continued.

Moreover, in the application of the TM bias, the repetition frequencyfor turning on and off is synchronized with the timing of detecting thecounter bias current in the counter bias current detecting circuit 203for control only using values when turned on, so that automatic controlis made possible.

According to the embodiment, in the parallel plate plasma apparatususing a dielectric material such as silica for the shower plate, even inthe case where the etching process configured of multiple steps underplasma conditions different from each other and the application of theconditions are performed for a first time, it is possible to eliminatethe necessity of studying the maximum values of the resonance point andthe bias current in advance, to reduce malfunctions caused by changingthe processing condition, to shorten turn around time (TAT), and toimprove the reproducibility of uniformity. At this time, when theinitial value of the variable capacitor 202 is set to a value of thecapacitance smaller than the resonating capacitance, automatic controlcan be performed without degrading uniformity in searching for theresonance point.

As described above, the embodiment is described in which the counterbias current detecting circuit 203 detects the counter bias current forautomatic control. However, also in the case of monitoring the voltageacross the earth and the point on the passage through which the counterbias current passes (a reference numeral 208 in FIG. 2, for example) ormonitoring the voltage across the resonant coil 201, the behaviors of apeak-to-peak voltage 402 of the counter bias and the variable capacitor202 are identical to the behavior of the counter bias current asillustrated in FIG. 4. Therefore, similar control can be performed eventhough the counter bias voltage value is used for the monitor signal.

Moreover, it may be fine that an impedance monitor is inserted betweenthe point 208 and the resonant coil 201 in FIG. 2 and the variablecapacitor 202 is controlled based on the detected impedance information.In this case, it may be fine that the point at which the reactance thatis an imaginary component of the impedance is zero is searched insteadof searching for the maximum value of the bias current. In theapplication of the TM bias, control can be performed in which theimpedance monitor is synchronized with the timing at which the biascurrent is turned on for control using the impedance when the biascurrent is turned on.

The case is described in the control flowchart of FIG. 3 where thetrigger to start automatic matching is the timing at which the biascurrent exceeds the threshold. However, when the trigger is changed to atrigger signal outputted from the etching apparatus side, automaticcontrol can be started after finishing the high transient phenomenon ofthe startup of the power supply, for example, so that malfunctionscaused by the transient phenomenon in ignition can be suppressed.Similarly, when it is permitted to separately set waiting time untilstarting the operation after the trigger signal is inputted from theapparatus side or after the bias current exceeds the threshold also inthe counter bias control mechanism, the apparatus can meet all theprocess conditions.

Also for the method for controlling the harmonic short circuit fine tunecapacitor 205, similar control is performed as the bias of the principalcomponent using the monitor result at the harmonic current detectioncircuit 207 and the automatic harmonic matching unit 209, so that theuniformity can be further improved.

Second Embodiment

A second embodiment of the present invention will be described withreference to FIGS. 5 to 7. It is noted that points described in thefirst embodiment but not described in the second embodiment can also beapplied to the second embodiment unless otherwise specified.

In the embodiment, an embodiment will be described below in which evenin the case where an electrostatic capacitance to resonate with a biascurrent changes in the steps such as the end point determination step,the changes can be followed. In order to implement the embodiment, inaddition to monitoring a counter bias current, a radio frequency biascurrent detecting unit 124 detects phase information about a radiofrequency bias current, and inputs the information to a resonancecontrol circuit 127.

In this operation, a counter bias current detecting circuit 203 alsoacquires phase information about the counter bias current, and inputsthe information to the resonance control circuit 127. The resonancecontrol circuit 127 calculates the difference between the phase of thecounter bias current and the phase of the radio frequency bias currentoscillated in plasma, and controls the variable capacitance based on theresult.

FIG. 5 is a graph of the dependence of the phase difference between thecounter bias current and the radio frequency bias current on thevariable capacitance. It was newly discovered that the position at whichthe bias current becomes the maximum is the position at which the phasedifference is at an angle of −90°. Since it is known by experiment thatthis phase difference is constant regardless of plasma conditions, themonitor value of this phase difference is controlled so as to be matchedwith the target value, and transient changes can be followed as well. Itis noted that a reference numeral 501 denotes the peak-to-peak currentof the counter bias, and a reference numeral 503 denotes a phasedifference in resonance.

FIG. 6 is a flowchart of phase difference detection according to theembodiment based on this principle. The process is as described in thefirst embodiment until starting automatic control (Steps S12 to S14correspond to Steps S1 to S3).

When a bias current is detached to start control (S15), a variablecapacitor 202 is adjusted for the phase difference set on the etchingapparatus side based on the relationship in FIG. 5 (S16). At this time,it is necessary to place a preset position 403 within −80 pF from theresonance point. This is because the phase difference is always reducedas the capacitance of the variable capacitor is increased in the regionin which the preset position is placed within 80 pF.

According to the relationship illustrated in FIG. 5, in the case wherethe monitored phase difference is smaller than the permitted value ofthe set value, the variable capacitor 202 is reduced, whereas in thecase where the monitored phase difference is greater than a set value502, the variable capacitor 202 is increased. The capacitance of thevariable capacitor 202 is then changed in such a way that the monitorvalue falls within the permitted value of the set value (S17).

In this control, as similar to the case of the first embodiment, sincethe capacitance smaller than the capacitance at a resonance point 405has a small amount of change in uniformity for the phase difference atthe set value 502, the phase difference is set greater than that at thepoint at an angle of −90°, which can provide more stable performanceagainst a variation over time, for example. Subsequently, in Step 18(S18), it is confirmed whether to continue discharge in the subsequentstep. In the case where it is necessary to continue discharge in thesubsequent step, the process is returned to Step 13 (S13). In the casewhere it is unnecessary to continue discharge in the subsequent step, itis confirmed whether the bias current is smaller than the set thresholdin Step 19 (S19). In the case where the bias current is greater than theset threshold, the process is returned to Step 14 (S14). In the casewhere the bias current is smaller than the set threshold, the process isfinished (S20).

As described above, according to the embodiment using phase differencedetection, it is possible to directly reach the target value withoutexceeding the absolute value of a counter bias current or the variablecapacitance of resonance, which are varied depending on the plasmaconditions, and to automatically follow changes in the bias resonancepoint and the resonance position (the plasma impedance) as indetermining the end point. It is noted that the method is alsoapplicable to multistep etching.

It is noted that as similar to the first embodiment, the control methodis similar when control is performed not only by the phase differencebetween the bias currents but also by the phase difference between thebias voltages. However, the phase difference at the resonance point ischanged depending on the position of the voltage to be measured, and thephase difference is not always at an angle of −90°, so that it isnecessary to check phase differences in advance according to theconfiguration of an apparatus for use.

As described above, for the method descried in the first and secondembodiments, the example is described in which the source power supply101 at 200 MHz and the RF bias power supply of magnetic field VHF plasmaat 4 MHz are mounted. However, the method is also applicable to aparallel plate apparatus (a so-called CCP apparatus) with no magneticfield as illustrated in FIG. 7. The apparatus in FIG. 7 is configured inwhich a source power supply 101 is connected on the wafer stage side anda shower plate 116 to be the surface of a counter earth electrode 701 isformed of a dielectric material. The method is similarly applicable byconnecting a counter bias control mechanism 104 for a source powersupply on the counter earth electrode 701 side.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIGS. 8 to 15. It is noted that points described in thefirst or second embodiment but not described in the third embodiment canalso be applied to the third embodiment unless otherwise specified.First, a plasma processing apparatus mounted with a counter bias controlmechanism that embodies a cleaning method of a plasma processing methodaccording to the embodiment will be described. FIG. 8 is a verticalcross sectional view of a parallel plate magnetic field VHF dry etchingapparatus.

A vacuum container of the dry etching apparatus includes an etchingchamber 108 for a plasma processing chamber, an earth internal cylinder107, a silica top plate 111, a VHF radiation antenna 115, a vacuum pump,and a pressure control valve (both of them are not illustrated in FIG.8).

Etching gases pass through a mass flow controller and a stop valve (bothof them are not illustrated in FIG. 8), and pass through a gas inletport A 109 and a gas inlet port B 112. The gases are distributed whilepreventing the gases from being mixed using a gas distribution plate114, and introduced from regions of a shower plate 116 concentricallydivided into two parts into the etching chamber. The gases thusintroduced are dissociated from each other by energy of electromagneticwaves applied from a plasma generating unit, and plasma is generated andmaintained.

This plasma generating unit includes a source power supply 101 of a VHFwave of 200 MHz, a source electromagnetic wave matching unit 102, and amagnetic field generating unit formed of an electromagnet A 105 and anelectromagnet B 106. These two electromagnets are used to uniformize theplasma generation distribution. The generated magnetic field is at 10 mTor less near the shower plate 116. VHF waves oscillated from the sourcepower supply 101 pass through the source electromagnetic wave matchingunit 102, and are introduced into the VHF radiation antenna 115 at aposition opposite to a wafer stage 120. The VHF radiation antenna 115 iselectrically isolated from the etching chamber 108 using the silica topplate 111.

An Si wafer 117 is placed on the wafer stage 120, including a stack ofetched materials and mask materials such as a silicon oxide film,silicon nitride film, Poly-Si (polysilicon) film, resist film,anti-reflective film, TiN film, tungsten film, Ta compound film, and Hfoxide film. The wafer stage 120 includes a focus ring 118 and asusceptor 119 in a ring shape disposed as covering the outercircumferential side and the side wall of the surface on which the Siwafer 117 is placed. The wafer stage 120 can control a plurality ofportions on the wafer stage 120 at different predetermined temperaturesusing a plurality of temperature control units, for example, (notillustrated in FIG. 8). The wafer stage 120 applies a direct currentvoltage ranging from −2,000 to +2,000 V generated using an electrostaticchuck (ESC) direct current power supply 122 to electrostatically chuckthe Si wafer 117 in etching processing, fills He of an excellent heattransfer efficiency in a gap between the Si wafer 117 and the waferstage 120, and controls the back surface pressure of the Si wafer 117.For the shower plate 116, silica, sapphire, or yttria was used, whichhave corrosion resistance against gasses and do not cause foreignsubstance emission. Since the shower plate 116 is in intimate contactwith the gas distribution plate 114 and the VHF radiation antenna 115using screws, for example, an excessive temperature increase can besuppressed by adjusting the temperature of a cooling medium for the VHFradiation antenna 115.

The wafer stage 120 is connected to an RF bias matching unit 121 and toa 4-MHz RF bias power supply 123 that leads ions from plasma to the Siwafer 117 and controls ion energy.

Such an RF bias power supply including a time modulation (sometimesdenoted as TM) function was used for the RF bias power supply 123, inwhich power can be outputted in a range of about one watt at the lowestto about four kilowatts at the maximum equivalent to the emission ofcontinuous sine waves to an object to be processed in a diameter of 12inches and on-off modulation is performed in a range of one hertz to tenkilohertz in order to obtain the effects of a reduction in charge updamage (electron shading) and improved vertical processability.

A radio frequency bias current applied to the wafer stage 120 propagatesthrough the inside of plasma toward the earth internal cylinder 107disposed as an earth on the inner wall of the etching chamber 108through a plasma sheath on the Si wafer 117. For the earth internalcylinder 107, such a conductive material is used as a conductivematerial of a low contamination or as a conductive material including athermal sprayed material of a low reactivity with etching plasma throughwhich a radio frequency passes, in order to reduce contamination in theapparatus and foreign substances.

In the parallel plate magnetic field VHF etching apparatus, in theembodiment, a counter bias control mechanism 104 is mounted through afilter unit 103 in order that a bias is transmitted to the VHF radiationantenna 115 side opposite to the wafer stage 120 to control the degreeof confinement of the bias electric field for improving etchinguniformity. The filter unit 103 includes a highpass filter (HPF) thatprevents an RF bias of 4 MHz and the third-order harmonic of the RF biasfrom passing on the source power supply side and a lowpass filter (LPF)that flows only an RF bias frequency to the earth side. It is noted thata reference numeral 110 denotes a cooling medium inlet, a referencenumeral 113 denotes a cooling medium outlet, a reference numeral 124denotes a radio frequency bias current detecting unit, a referencenumeral 125 denotes a wafer stage elevating mechanism, a referencenumeral 126 denotes a silica ring, a reference numeral 127 denotes aresonance control circuit, a reference numeral 128 denotes a yoke, areference numeral 131 denotes an EPD (End Point Detector) window, and areference numeral 133 denotes a shield plate. The radio frequency biascurrent detecting unit 124 may be disposed in the RF bias matching unit121.

FIG. 9 is a diagram of the configuration of the counter bias controlmechanism 104. The counter bias control mechanism 104 is configured of aserial resonant portion formed of a resonant coil 201 and a variablecapacitor 202 having a moderate withstand voltage, a counter biascurrent detecting circuit 203, and a resonance control circuit 127. Inconsideration of the electrostatic capacitance (C_(sp)) of the silicashower plate 116 and the electrostatic capacitance (C_(sh)) of a sheathformed on the shower plate, the inductance (L) of the resonant coil 201and the electrostatic capacitance (C_(v)) of the variable capacitor 202are selected using the relationship between Equations (1) to (3)described in the first embodiment.

Moreover, a plurality of sets of a harmonic short circuit coil 204 and aharmonic short circuit fine tune capacitor 205 according to the harmonicorder is inserted in parallel with a circuit formed of the resonant coil201 and the variable capacitor 202, and the impedance of a harmoniccomponent generated when passing through the plasma sheath on the VHFradiation antenna 115 can also be reduced, so that etching can beuniformized for wider plasma conditions. Furthermore, the electriccurrent values of a plurality of harmonic components are monitored usinga harmonic current detection circuit 207, so that information about theplasma density and the electron temperature can be obtained as well, anda change in the state of the apparatus can be detected more accurately.It is noted that a reference numeral 206 denotes an automatic matchingunit, a reference numeral 208 denotes a voltage measurement point, and areference numeral 209 denotes an automatic harmonic matching unit.

The embodiment relates to a plasma cleaning method using the counterbias control mechanism 104 disposed on the parallel plate plasmaprocessing apparatus thus configured. Plasma cleaning is necessary forstabilizing mass production in the etching process in the process stepof removing etching reaction products attached in the etching chamber inetching processing. Plasma cleaning is appropriately inserted betweenindividual wafers or lots after the etching process.

For example, for a cleaning gas in etching Si using Cl₂ or HBr, such agas is used that oxygen or nitrogen, for example, is mixed in a gas tosupply fluorine such as SF₆, NF₃, and CF₄. For a cleaning gas in etchingSiO₂ or SiN using a fluorocarbon gas, such a gas is used that O₂ or N₂is mixed, or H is mixed in some case. For a cleaning gas in etching Al,Ti, or Hf, for example, a gas such as Cl₂, HCl, and HBr is used.

FIG. 10 is measured data that a change in a counter bias current Ipp 302is measured at the counter bias current detecting circuit 203 when theelectrostatic capacitance of the variable capacitor 202 in the counterbias control mechanism 104 is changed. It is shown that since the pointat which the bias current becomes the maximum is the resonance point,the counter bias current value takes the maximum value with respect tothe capacitance of the variable capacitor 202. Moreover, the capacitanceof the variable capacitor at the maximum value and the maximum value ofthe counter bias current are changed in the range of about 50 pF whenthe electrical capacitance (C_(sh)) of the sheath formed on the showerplate is changed, that is, when the plasma conditions (the output powerof the source power supply 101, the processing pressure, and the powerof the RF bias power supply 123, for example) are changed. A referencenumeral 301 denotes a dissonance point, and a reference numeral 303denotes a resonance point. Furthermore, in a graph in FIG. 10, althougha counter bias voltage Vpp 304 is also plotted at the voltagemeasurement point 208 in the counter bias control mechanism, thebehavior is matched with the behavior of the counter bias current Ipp302. Thus, in the following, the description will be given as the casewhere the counter bias voltage Vpp 304 is detected.

FIG. 11 is the in-plane distribution of the rate of an oxide filmattached on the shower plate 116 when the counter bias control mechanism104 is resonating (a reference numeral 410 in FIG. 11) and when thecounter bias control mechanism 104 is not resonating (a referencenumeral 420 in FIG. 11) where a SF₆/O₂ gas is at 8 Pa and the RF biaspower is at 100 W. It was found that the etching rate of an oxide filmin simulating the wearing out of the silica shower plate is about 20nm/min in the plane on average in dissonance whereas the etching rate isincreased twice or more at the resonance point as the oxide film rate isabout 45 nm/min.

This is because the counter bias control mechanism 104 is resonated toreduce the reactance on the VHF radiation antenna 115 side, so that theion current and the electron current are accelerated from plasma in thesheath and the currents flow in. With the use of this principle, thecounter bias control mechanism 104 can be resonated in cleaning to causean ion assist reaction on the silica shower plate 116, so that thecleaning rate can be dramatically improved.

The timing chart of the cleaning method for the dry etching apparatusillustrated in FIG. 8 to which the present invention is applied will bedescribed with reference to FIG. 12. FIG. 12 is a sequence chart of themeasured results of the time variation of light emission intensity 511at a wavelength of 440 nm measured through the EPD window 131, anopening degree 512 of the pressure control valve (not illustrated inFIG. 8), an RF bias voltage Vpp 513 detected at the RF bias matchingunit 121, and a counter bias voltage Vpp 514 detected at the voltagemeasurement point 208 in the counter bias control mechanism undercleaning processing after etched using a fluorocarbon gas and the mannerof control of the variable capacitor 202 in the counter bias controlmechanism. The following is the cleaning conditions, where O₂ is at 800ccm, a pressure is at 4 Pa, the output of the source power supply 101 isat 800 W, and the output of the RF bias power supply 123 is at 1,000 W.

When the plasma light emission intensity 511, the pressure control valvethe position 512, or the control valve opening degree is fixed, whichare previously existing means for detecting the cleaning end point,relatively long time constants are observed for a change in thepressure, the RF bias voltage Vpp 513, or the time variation of theplasma impedance detected on the RF bias side, whereas the time constantfor the counter bias voltage Vpp 514 used in the present invention isshort. This is because the cleaning end points are detected on theentire boundary contacting plasma in the previously existing detectionmethod, whereas the time variation of the counter bias voltage Vpp 514is short because the cleaning end point is detached on the boundarysurface on the shower plate 116 side in the entire boundary.

Therefore, an end point 515 for removal of the attachment on the showerplate is determined at time at which the absolute value of the amount ofchange Vpp (A)−Vpp (B) in the counter bias voltage Vpp value betweentime A and time B becomes smaller than the set value for a specifiednumber of times or more or determined at the inflection point of thecounter bias voltage Vpp value (at the point at which the secondarydifference of Vpp reaches zero). After a lapse of preset over cleaningtime 519 from the timing, the capacitance of the variable capacitor 202of the counter bias control mechanism 104 is adjusted from a variablecapacitor position 517 in resonance to a position 518 for the variablecapacitor in dissonance.

As a result of the control, the monitor value of the counter biasvoltage Vpp is changed as a dotted line (a dotted line 520 in FIG. 12).With this manipulation, the conditions can be changed in such a way thatthe conditions in which the cleaning effect of the shower plate due toan ion assist reaction is maximized are first used and then theconditions in which the degree of the wearing out of the shower plate isreduced in an ion impact are used, so that it is possible to reduce thefrequency of replacing the shower plate, which enables a reduction inCoC and the extension of MTBM. It is noted that a reference numeral 516is the end point of chamber cleaning.

Although a larger amount of change from the resonance point to thedissonance point is preferable, this is varied depending on thedielectric constant and thickness of the shower plate 116 and theelectrical passage from the VHF radiation antenna 115 to the counterbias control mechanism 104. In the embodiment, a change of 50 pF or morewas sufficient.

The cleaning end point determination control like this is feasible usingan end point determination circuit 191 illustrated in FIG. 13. In otherwords, in the control parameters monitored in etching or in cleaning,parameters sensitive to the time variation for cleaning are extracted(the monitored parameters in FIG. 12, for example), the monitor signalof the counter bias voltage Vpp is calculated as described above basedon the signals of the monitored parameters, and the end point of theremoval of the attachment on the shower plate is determined. The endpoint determination circuit 191 may be externally installed on apreviously existing device, or can be implemented by changing controlsoftware for a previously existing device when monitor signals exist.

FIG. 14 is a graph of the oxidization film etching rate in the centerpart of the shower plate when the RF bias power is changed in resonance(a reference numeral 710 in FIG. 14) and in dissonance (a referencenumeral 720 in FIG. 14). In resonance, it is shown that the oxide filmrate on the shower plate is almost linearly increased in associationwith an increase in the RF bias power. Therefore, the method forcontrolling ion energy on the shower plate can be implemented byresonating the counter bias control mechanism 104 to adjust the RF biaspower. Only the RF bias power is adjusted, so that ion energy on theshower plate can be changed without operating the variable capacitor 202of the counter bias control mechanism 104, which is advantageous toprolong the lifetime of the variable capacitor.

Moreover, the in-plane distribution of the cleaning rate on the showerplate is matched with the plasma distribution, so that control isfeasible by resonating the counter bias control mechanism 104 to adjustthe electric currents of the electromagnet A 105 and the electromagnet B106. It may be possible that with the use of these characteristics,after determining the cleaning end point of the shower plate, the coilcurrent or the RF bias power is changed for over cleaning for a certaintime period to improve the efficiency of removal of the attachment onthe surface.

The example in FIG. 12 shows the example in which the attachment tendsto be removed as fluorocarbon attachments are removed using oxygen. Inthe case of removing AlF₃, HfF₄, and TiO₂, for example, an ion assistreaction is necessary. In the case of cleaning these compounds, a mixedgas is used in which a gas including reductive H or B (HCl and BCl₃, forexample) that easily breaks coupling such as Al—F and Ti—O is mixed witha gas that increases the volatility of a reaction product with Al, Hf,and Ti in Cl₂, HBr, and SiCl₄, for example. The counter bias controlmechanism 104 is then resonated to apply an RF bias of 100 W or more toan Si wafer, so that the attachment on the shower plate can beefficiently removed.

In the embodiment, the magnetic field parallel plate etching apparatusincluding a dielectric in the upper electrode as illustrated in FIG. 8is described. Similar effects can be obtained in cleaning a parallelplate etching apparatus with no magnetic field as illustrated in FIG.15, in which the circuit constant of a counter bias control mechanism104 is changed according to Equations (1) to (3) depending on thefrequency of a source power supply 101 or an RF bias power supply 123for use. The control of the cleaning distribution in this case isconducted using the power of the source power supply 101, the processpressure, and the power of the RF bias power supply 123.

Moreover, as illustrated in FIG. 15, the attachment on a silica internalcylinder 804 can be similarly cleaned in which an etching chamber 108 iselectrically insulated from a base flange using an insulation ring A 801and an insulation ring B 803, an RF bias current passes through a sourcefrequency ground circuit 802 through the silica internal cylinder 804,and a counter bias control mechanism 104 controls the RF bias currentconnected to the etching chamber 108.

According to the embodiments as described above, it is possible toprovide a plasma processing method that reduces the wearing out of thedielectric ceramic on the upper antenna side as in a CCP etchingapparatus, for example, including the counter bias control mechanism andimproves MTBM and CoC of the apparatus.

As described above, the invention of the present application isdescribed in detail. The following is the main aspects of the presentinvention.

(1) A plasma processing method using a plasma processing apparatusincluding a plasma processing chamber configured to plasma-process anobject to be processed, a first flat electrode configured to emit aradio frequency into the plasma processing chamber, a first radiofrequency power supply configured to supply radio frequency power to thefirst electrode, a second electrode opposite to the first electrode andon which the object to be processed is placed, a second radio frequencypower supply configured to supply radio frequency power to the secondelectrode, and a control mechanism configured to control a radiofrequency current carried through the first electrode or a radiofrequency voltage applied to the first electrode, the method including:a first step of setting a reactance of a variable element included inthe control mechanism to an initial value; a second step of detectingthe radio frequency current or the radio frequency voltage; a third stepof setting the reactance of the variable element to a reactance value sothat the radio frequency current takes a maximum value or the radiofrequency voltage takes a maximum value and fixing the reactance of thevariable element to the set reactance value; and a fourth step ofplasma-processing the object to be processed.(2) A plasma processing method using a plasma processing apparatusincluding a plasma processing chamber configured to plasma-process anobject to be processed, a first flat electrode configured to emit aradio frequency into the plasma processing chamber, a first radiofrequency power supply configured to supply radio frequency power to thefirst electrode, a second electrode opposite to the first electrode andon which the object to be processed is placed, a second radio frequencypower supply configured to supply radio frequency power to the secondelectrode, and a control mechanism configured to control a radiofrequency current carried through the first electrode or a radiofrequency voltage applied to the first electrode, the method including:a first step of detecting a phase difference between a radio frequencycurrent carried through the second electrode and a radio frequencycurrent carried through the first electrode or a phase differencebetween a radio frequency voltage applied to the second electrode and aradio frequency voltage applied to the first electrode; a second step ofcontrolling a reactance of a variable element included in the controlmechanism so that the detected phase difference takes a phase differencevalue matched with a maximum value of the radio frequency currentcarried through the first electrode or a maximum value of the radiofrequency voltage applied to the first electrode; and a third step ofplasma-processing the object to be processed.(3) A plasma processing method using a plasma processing apparatusincluding a plasma processing chamber configured to plasma-process anobject to be processed, a first flat electrode configured to emit aradio frequency into the plasma processing chamber, a first radiofrequency power supply configured to supply radio frequency power to thefirst electrode, a second electrode opposite to the first electrode andon which the object to be processed is placed, a second radio frequencypower supply configured to supply radio frequency power to the secondelectrode, and a control mechanism configured to control a radiofrequency current carried through the first electrode or a radiofrequency voltage applied to the first electrode, the method including:a first step of setting a reactance of a variable element included inthe control mechanism to an initial value; a second step of detectingthe radio frequency current or the radio frequency voltage; a third stepof setting the reactance of the variable element to a reactance value sothat the radio frequency current takes a maximum value or the radiofrequency voltage takes a maximum value and fixing the reactance of thevariable element to the set reactance value; and a fourth step ofplasma-cleaning the inside of the plasma processing chamber after thethird step.(4) A plasma processing method using a plasma processing apparatusincluding a plasma processing chamber configured to plasma-process anobject to be processed, a first flat electrode configured to emit aradio frequency into the plasma processing chamber, a first radiofrequency power supply configured to supply radio frequency power to thefirst electrode, a second electrode opposite to the first electrode andon which the object to be processed is placed, a second radio frequencypower supply configured to supply radio frequency power to the secondelectrode, and a control mechanism configured to control a radiofrequency current carried through the first electrode or a radiofrequency voltage applied to the first electrode, the method including:a first step of detecting a phase difference between a radio frequencycurrent carried through the second electrode and a radio frequencycurrent carried through the first electrode or a phase differencebetween a radio frequency voltage applied to the second electrode and aradio frequency voltage applied to the first electrode; a second step ofcontrolling a reactance of a variable element included in the controlmechanism so that the detected phase difference takes a phase differencevalue matched with a maximum value of the radio frequency currentcarried through the first electrode or a maximum value of the radiofrequency voltage applied to the first electrode; and a third step ofplasma-cleaning the inside of the plasma processing chamber after thesecond step.

It is noted that the present invention is not limited to the foregoingembodiments, and includes various exemplary modifications. For example,the forging embodiments are described in detail for easily understandingthe present invention. The present invention is not always limited toones including all the described configurations. Moreover, a part of theconfiguration of an embodiment can be replaced by the configuration ofanother embodiment, and the configuration of another embodiment can beadded to the configuration of an embodiment. Furthermore, a part of theconfigurations of the embodiments can be added with, deleted from, orreplaced by the other configurations.

What is claimed is:
 1. A method for controlling a plasma processingapparatus including a plasma processing chamber in which an object to beprocessed is plasma-processed, a first electrode which emits a radiofrequency into the plasma processing chamber, a first radio frequencypower supply which supplies radio frequency power to the firstelectrode, a second electrode arranged to face the first electrode andon which the object to be processed is placed, a second radio frequencypower supply which supplies radio frequency power to the secondelectrode, the method comprising the steps of: detecting a radiofrequency current flowing from the second electrode toward the firstelectrode or a radio frequency voltage on a path in which the radiofrequency current flows; and controlling a reactance for controlling thedetected radio frequency current or the detected radio frequency voltageso that the detected radio frequency current or the detected radiofrequency voltage takes a value of the resonance point.
 2. The methodfor controlling a plasma processing apparatus according to claim 1,wherein the initial value of the reactance is greater than the value ofthe resonance point so that the radio frequency current takes a maximumvalue or the radio frequency voltage takes a maximum value.
 3. A methodfor controlling a plasma processing apparatus including a plasmaprocessing chamber in which an object to be processed isplasma-processed, a first electrode which emits a radio frequency intothe plasma processing chamber, a first radio frequency power supplywhich supplies radio frequency power to the first electrode, a secondelectrode arranged to face the first electrode and on which the objectto be processed is placed, a second radio frequency power supply whichsupplies radio frequency power to the second electrode, the methodcomprising steps of: detecting a first phase difference between a firstradio frequency current flowing from the second radio frequency powersupply toward the second electrode and a second radio frequency currentflowing from the second electrode toward the first electrode or a secondphase difference between a first radio frequency voltage applied to thesecond electrode and a second radio frequency voltage on a path in whichthe second radio frequency current flows, and controlling a reactancefor controlling the second radio frequency current or the second radiofrequency voltage based on the detected first phase difference or thedetected second phase difference.
 4. The method for controlling a plasmaprocessing apparatus according to claim 3, wherein the value of thefirst or second phase difference is a value within a desired permissiblevalue with respect to an angle of 90 degrees.
 5. The method forcontrolling a plasma processing apparatus according to claim 3, whereinthe reactance is a variable capacitor.